The isolation by our laboratory and others of the gene for the precursor of the Alzheimer's disease amyloid polypeptide, has made it possible to begin dissecting at a molecular level the processes whereby this normal protein may become altered in Alzheimer's disease. The sequence of events which leads to the deposition of the small self-aggregating amyloid peptide in Alzheimer's disease is not known. A key question concerns the causal relationship of amyloid to the pathology of Alzheimer's disease. Projects are proposed to address these questions. In the original application, we proposed to do a detailed analysis of amyloid protein precursor (APP) transcription in defined regions of Alzheimer's disease and normal brains, to test the hypothesis that the development of pathology in Alzheimer's disease is related to changes in the expression of the APP mRNAs. This specific aim has been completed: we were able to show that the mRNA encoding APRP-563, an APP-related mRNA lacking the amyloid-encoding sequence, is specifically elevated in pathologically affected regions of Alzheimer's disease brain. We have shown, by the construction and characterization of recombinant transfected cell lines expressing particular domains of APP, that the carboxyterminal 105 amino acids of the human amyloid protein precursor is neurotoxic. Studies are proposed to examine the relationship of the neurotoxicity of this fragment (termed AB1) to Alzheimer's disease pathology, by analyzing the pattern of segregation of the microtubule associated protein tau in neurons treated with AB1, and by assaying for differential vulnerability of CA1 hippocampal neurons to AB1 neurotoxicity. Characterization of AB1 neurotoxicity will include definition of the mechanism of glial protection of neurons against AB1 toxicity, determination of the vulnerability of hippocampal neurons from rats of various ages to AB1 neurotoxicity, and assessment of the minimum exposure time of neurons to the AB1 conditioned medium that is necessary to cause their subsequent degeneration. We recently discovered that the neurotoxic AB1 fragment can, under the appropriate conditions, be trophic: experiments to quantify and characterize this trophic effect, and to relate it to the neurotoxicity, are described. Both genetic and pharmacologic methods will be utilized in an attempt to neutralize or block the neurotoxicity of the carboxyterminal 105 amino acids of AB1. The development of alternate methods of synthesis of this AB1 fragment will facilitate the performance of the proposed studies. Studies to follow up on our recent finding that the AB1 fragment binds specifically to the surface of NGF-differentiated PC12 cells but not to undifferentiated PC12 cells, are proposed. Finally, we show that mouse brains transplanted with AB1-transfected PC12 cells demonstrate progressive neurodegeneration in the region of the transplant, and show immunoreactivity with the Alz50 antibody. The possibility of developing these transplanted mice as an animal model for Alzheimer's disease is proposed.